(a) Field of the Invention
The present invention relates to an ink jet recording device and, more particularly, to an ink jet recording device wherein recording is effected by ejecting colored particles in pigmented ink onto a recording sheet
(b) Description of the Related Art
Non-impact recording method attracts a large attention in a printing technology for its low noise during a recording operation. Among other non-impact recording methods, an ink jet recording method has several advantages such as direct and high-speed printing onto a recording sheet such as a plain paper. A variety of proposals are presented heretofore for improving ink jet recording devices implementing the ink jet recording method.
In a conventional ink jet recording device, colored particles in a pigmented ink received in an ink chamber are ejected from an ink jet slit by using an electrophoretic force and an electrostatic force to form images on a recording sheet based on print data. In the ink jet recording device, if the density or concentration of the colored particles in the pigmented ink is reduced as a result of the consumption of the colored particles, there arises a problem in that a stable printing cannot be obtained.
The problem reduction of the concentration of the colored particles in the pigmented ink may be solved by replenishment of the concentrated pigmented ink. Patent Publication JP-A-4(1992)-106573 proposes a replenishment device for replenishing a developer in an photocopying machine. FIG. 1 shows a schematic block diagram of the proposed replenishment device, wherein the device comprises an developer tank 10 communicated with a chamber in the recording head (not shown in the drawing), an optical densitometer 15 immersed in the developer 11 received in the developer tank 10, a replenishment tank 16 for receiving therein concentrated developer 12 for replenishment, and a controller 24 for controlling the amount of concentrated developer 12 to be replenished from the replenishment tank 16 through a tube 13 to the developer tank 10 by controlling a control valve 14.
The control unit 24 comprises a comparator 23, a reference concentration signal generator 22, and a counter 21 for counting the number of copied sheets to supply a count signal 18 to the reference concentration signal generator 22. The reference concentration signal generator 22 calculates, based on the count signal 18 and a normal reference concentration to be applied, a corrected reference concentration value, which is supplied to the reference terminal of the comparator 23 as a reference concentration signal 19. The concentration of the toner in the developer 11, which is detected by the optical densitometer 15, is supplied to the signal terminal of the comparator 23 as a detected concentration signal 17.
The comparator 23 compares the detected concentration signal 17 against the reference concentration signal 19 to deliver a valve control signal 20 to the control valve 14 to open the control valve 14 if the detected concentration signal 17 is lower than the reference concentration signal 19, thereby replenishing the concentrated developer 12 from the replenishment tank 16 to the developer tank 10.
In the proposed device, the toner concentration in the developer 11 can be maintained roughly at a constant level by replenishing the concentrated developer 12. However, the control of the toner concentration at a precise level by adjusting the valve opening is difficult in fact.
Moreover, the reference concentration signal for the comparator is corrected simply based on the number of the recorded sheets. However, the amount of the toner in the developer consumed by recording is not precisely calculated based on the number of recorded sheets.
Therefore, it is difficult to expect a fine control of the toner concentration in the developer by the configuration of the proposed device in the copying machine.